Indirect Gas-Fired Make-Up Air Unit
Some spaces cannot have any trace of combustion in the air your unit supplies. Food plants, labs, and pharma facilities need clean tempered air, and that need rules out direct-fired heating. Indirect gas-fired make-up air solves it. A sealed heat exchanger keeps the flue gases separate, so the air you bring in stays clean.
We spec indirect gas-fired make-up air units across multiple manufacturer lines and match the configuration to your exhaust volume, climate, and discharge target. Every unit is US-made and backed by the manufacturer’s warranty.
Have questions? Need a quote?
Authorized Indirect MUA Suppliers
We are the authorized distributors for the leading American manufacturers of indirect gas-fired make-up air units. We’ll be pleased to provide the ideal make up air unit for your application as authorized representatives.
For a fast quote or if you have inquiries about commercial or industrial MUA, get in touch with us.
How Indirect Gas-Fired Make-Up Air Units Work
Your supply air passes over a sealed heat exchanger, never through the flame. A gas burner heats the metal surface of that exchanger, and the outdoor air picks up heat as it crosses it. The combustion gases stay trapped inside and vent outside through a flue.
That separation is what sets indirect apart. A direct-fired unit fires the burner straight into the airstream, so nearly all the heat reaches the space, but the combustion products travel with it. Indirect gives up some of that efficiency in exchange for clean air, which is why it anchors so many heated make-up air builds for sensitive spaces.
Indirect Gas-Fired MUA Specifications and Configurations
Sizing an indirect gas-fired unit starts with your exhaust volume, because the make-up air has to match it to hold building pressure. From there, your climate and target discharge temperature set the heating capacity you need. Run your numbers through our make-up air sizing calculator before you spec, then confirm the configuration against the ranges below.
| Specification | Typical Range |
|---|---|
| Airflow | 600 to 200,000 CFM by model |
| Heating input | 250,000 to 6,000,000 BTU/hr |
| Thermal efficiency | 80 to 90% |
| Temperature rise | 20°F to 100°F |
| Turndown | 2:1 staged, up to 30:1 modulating |
| Max discharge temperature | Up to 140°F |
| Fuel | Natural gas or propane |
| Mounting and discharge | Indoor or outdoor; down, horizontal, or upblast |
Advantages of Indirect Gas-Fired Make-Up Air
| Advantage | What It Means for You |
|---|---|
| Clean supply air | No combustion byproducts enter the airstream, so the air meets strict quality standards |
| Code compliance | Accepted in high-occupancy and sensitive spaces where direct-fired is not allowed |
| No added moisture | Combustion stays sealed, so the supply air stays dry |
| Fuel flexibility | Runs on natural gas or propane to fit your site |
| Wide capacity range | Scales from small commercial loads to large industrial volumes |
Disadvantages of Indirect Gas-Fired Make-Up Air
| Disadvantage | What It Means for You |
|---|---|
| Lower efficiency | Flue losses put it around 80 to 90%, below a direct-fired unit, which shows up on the gas bill |
| Higher equipment cost | The heat exchanger and flue add to the unit price compared with direct-fired |
| Larger footprint | The heat exchanger makes the cabinet bigger for the same heating load |
| Flue required | Venting the combustion gases adds to installation |
| Limited turndown on some units | Many offer only 2:1 modulation, which can loosen leaving-air-temperature control |
Indirect Gas-Fired MUA Features
- Sealed heat exchanger that keeps combustion fully separate from the supply air
- Power-vented flue that clears combustion gases even under negative building pressure
- Modulating or staged gas burner controls for leaving-air-temperature management
- Indoor or outdoor cabinet with down, horizontal, or upblast discharge
- Optional cooling coils for applications that need tempered air year-round
- Flame safeguard controls and BAS integration for monitoring and setpoint control
Where Indirect Gas-Fired Make-Up Air is Required
You reach for indirect-fired when the space cannot accept any combustion in the supply air. Code often makes that call for you in high-occupancy buildings, so confirm the local requirement before you spec.
- Food processing plants and commercial kitchens, where supply air cannot contaminate food or food-contact surfaces
- Pharmaceutical and laboratory spaces that hold tight air-quality control
- Healthcare facilities with strict indoor air standards
- Schools and other high-occupancy spaces where code calls for separated combustion
Why Engineers Spec Indirect Gas-Fired MUA With Us
You get a partner who specs the unit to your application, not a salesperson pushing one brand. We carry indirect gas-fired make-up air across multiple manufacturer lines, so the recommendation you get is the one that fits your exhaust volume, climate, and discharge target.
Our team reviews your requirements before quoting and helps you size the unit right the first time. That means fewer surprises at startup and a configuration that holds building pressure the way it should.
Every unit is US-made and backed by industry leading manufacturer warranties.
Call 847-262-3457 ext. 23 to talk through your application and get a quote on the right indirect gas-fired make-up air unit.
Have questions? Need a quote?
Frequently Asked Questions
It is a unit that heats incoming outdoor air with a sealed heat exchanger instead of an open flame. The burner fires inside the heat exchanger, and your supply air passes over the outside of it. The combustion gases vent outside through a flue, so they never mix with the air you bring into the building.
A direct-fired unit fires the burner straight into the airstream, so it puts combustion byproducts into the supply air. An indirect-fired unit keeps the two apart with a heat exchanger. You give up some efficiency, but you get clean tempered air. See our direct gas-fired make-up air units for a side-by-side comparison.
You need indirect-fired any time the space cannot have combustion products in the supply air. Code often requires it in high-occupancy buildings, so check your local requirement first. Food processing, pharma, labs, and healthcare spaces are the common cases.
Most indirect-fired units run between 80 and 90 percent thermal efficiency. Some heat is lost out the flue with the combustion gases, which is the trade-off for keeping the supply air clean.
Temperature rise typically ranges from 20°F to 100°F, with discharge often capped around 140°F. Turndown runs from 2:1 on staged burners up to 30:1 on large modulating units. Higher turndown holds your leaving-air temperature steadier as outdoor conditions swing.
Start with your exhaust volume, because the make-up air has to match it to keep building pressure balanced. From there, your climate and target discharge temperature set the heating capacity. Run your numbers through our make-up air sizing calculator to get in the right range before you spec.
Yes. You can add cooling to the same cabinet, usually with a direct expansion coil, chilled water coil, or evaporative section. That gives you tempered air in both heating and cooling seasons from one unit.
Most run on natural gas or propane, and some support dual fuel. The right choice depends on what your site has available.
We do both. We carry indirect gas-fired make-up air across several manufacturer lines, help you size and configure the right one, and supply it. You get one source for the recommendation and the equipment, not a catalog to sort through alone.
Every unit is US-made and backed by strong manufacturer warranties. If a warranty issue ever comes up, we help you work through it so you are not dealing with the manufacturer on your own. Call 847-262-3457 ext. 23 to talk through your application.